backport from libyaml-1.1.6

libyaml <= 0.1.5 is vulnerable to CVE-2014-2525. I created patch for libyaml-0.1.6 fixes.

 * http://www.ocert.org/advisories/ocert-2014-003.html
 * http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-2525